My first time hurt, and I had been toying with my tailpipe long before that so I had plenty of practice. Getting past the sphincter is always a bit painful, but once the pleasure kicks in it's paradise. Make sure if a guy is going to fuck you that your hole is clean: learn about enemas, get a soapy finger up there while showering rinse well. If you have the type of shower head that's attached to the wall, get a hand held shower, that makes it very easy to keep a clean ass. Don't eat a large meal hours before getting rammed.
The best way to make bottoming easy is to use dildos or butt plugs often, whenever you jerk off is best. It can get tiring for your arm to be shoving a
Dildo in and out, especially while jerking. Get a
Dildo with a suction cup base, it's a life changer. You can stick it to most any surface (the shower wall is great, getting fucked in the shower is heaven) and then ride it hands free. Start off with a normal penis sized
Dildo (6 or 7 inches), starting off with a big
Dildo will hurt until you gain some experience. Think of getting fucked like driving a motorcycle: you don't just hop on and go without knowing what to do. Use LOTS of lube (if the
Dildo requires water-based, don't use oil based) and insert a little, pull almost all of it out, then insert further than last time. Keep repeating until it's buried to the balls and your eyes roll back in your head. If you have to grit your teeth so the entire house doesn't hear you cry out in joy, you're doing it right! Just don't quit, the pain of insertion is temporary and you will learn to endure it. Over time even the pain of getting split open by a big shaft feels amazing. All of us have the same internal organs, it's painful for everyone to learn to take it. But think about how many people love getting fucked in the ass: they all were virgins at one time. Sometimes I want my boyfriend to ease into my hole gently, other times he lubes me up and shoves it all in with one thrust and I LOVE it! So don't be surprised if you go from "take it out, it hurts!" to "FUCK ME HARDER! FASTER! OH GOD YES!". You be on your back with your legs behind your head in no time. And don't forget the joy of fucking a guy, try topping too!
One reason you might have had too much pain was the position you were in. Were you laying on your stomach and he was on top pumping away? You want to be in a position where he can't just slam it in all the way, you want control. Try riding him: sit down on it and you can take as much as you want. Make sure you jerk off when you get fucked, not only does it feel good, it takes your mind off any pain. The main reason getting fucked is so awesome is the orgasm. When you cum while getting shafted, it's the most intense orgasm ever. Some guys (myself included) can sometimes get rock hard and shoot an insane load hands free.